4x^2-9x-21=

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Solution for 4x^2-9x-21= equation:


Simplifying
4x2 + -9x + -21 = 0

Reorder the terms:
-21 + -9x + 4x2 = 0

Solving
-21 + -9x + 4x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
4 the coefficient of the squared term: 

Divide each side by '4'.
-5.25 + -2.25x + x2 = 0

Move the constant term to the right:

Add '5.25' to each side of the equation.
-5.25 + -2.25x + 5.25 + x2 = 0 + 5.25

Reorder the terms:
-5.25 + 5.25 + -2.25x + x2 = 0 + 5.25

Combine like terms: -5.25 + 5.25 = 0.00
0.00 + -2.25x + x2 = 0 + 5.25
-2.25x + x2 = 0 + 5.25

Combine like terms: 0 + 5.25 = 5.25
-2.25x + x2 = 5.25

The x term is -2.25x.  Take half its coefficient (-1.125).
Square it (1.265625) and add it to both sides.

Add '1.265625' to each side of the equation.
-2.25x + 1.265625 + x2 = 5.25 + 1.265625

Reorder the terms:
1.265625 + -2.25x + x2 = 5.25 + 1.265625

Combine like terms: 5.25 + 1.265625 = 6.515625
1.265625 + -2.25x + x2 = 6.515625

Factor a perfect square on the left side:
(x + -1.125)(x + -1.125) = 6.515625

Calculate the square root of the right side: 2.552572232

Break this problem into two subproblems by setting 
(x + -1.125) equal to 2.552572232 and -2.552572232.

Subproblem 1

x + -1.125 = 2.552572232 Simplifying x + -1.125 = 2.552572232 Reorder the terms: -1.125 + x = 2.552572232 Solving -1.125 + x = 2.552572232 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.125' to each side of the equation. -1.125 + 1.125 + x = 2.552572232 + 1.125 Combine like terms: -1.125 + 1.125 = 0.000 0.000 + x = 2.552572232 + 1.125 x = 2.552572232 + 1.125 Combine like terms: 2.552572232 + 1.125 = 3.677572232 x = 3.677572232 Simplifying x = 3.677572232

Subproblem 2

x + -1.125 = -2.552572232 Simplifying x + -1.125 = -2.552572232 Reorder the terms: -1.125 + x = -2.552572232 Solving -1.125 + x = -2.552572232 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.125' to each side of the equation. -1.125 + 1.125 + x = -2.552572232 + 1.125 Combine like terms: -1.125 + 1.125 = 0.000 0.000 + x = -2.552572232 + 1.125 x = -2.552572232 + 1.125 Combine like terms: -2.552572232 + 1.125 = -1.427572232 x = -1.427572232 Simplifying x = -1.427572232

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.677572232, -1.427572232}

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